The invention relates to improvements in apparatus for discharging fluids, and more particularly to improvements in apparatus for directing jets of a fluid, such as compressed steam, toward successive increments of a running web of paper or the like. Still more particularly, the invention relates to improvements in apparatus of the type disclosed in commonly owned U.S. Pat. Nos. 4,915,788 (granted Apr. 10, 1990) and 5,059,285 (granted Oct. 22, 1991) to Stefan H. Winheim. The disclosures of these patents are incorporated herein by reference.
The patents to Winheim disclose an apparatus wherein a housing defines a plurality of chambers each of which receives steam from a discrete valve. The housing has a wall which is adjacent one side of the path for movement of a running web of moisture-containing fibrous material. Such wall has numerous apertures which discharge jets of steam toward the running web. Additional walls of the housing are designed to cooperate with the apertured wall to completely enclose the chambers.
The purpose of the patented apparatus is to raise the temperature of the running web of fibrous material (e.g., in a paper making machine) and to thus promote expulsion of moisture from the web. The patented apparatus can be used with equal or similar advantage in certain types of paper finishing or processing machines, e.g., in so-called soft compact calenders wherein a running web of paper or the like is caused to advance through one or more nips each of which is defined by two neighboring calender rolls. It is often necessary to contact a running paper web with steam ahead of a nip in a soft compact calender wherein the web is to undergo a smoothing or another quality-improving action. The just outlined calenders employ soft rolls which are subject to wear and must be replaced or repaired at certain intervals. The period of time which is required to replace a damaged or spent soft roll in a soft compact calender is in the range of ten times n minutes wherein n normally equals or approximates two Thus, the treatment of a web must be interrupted for an interval of twenty minutes or so. In other words, the chambers of the aforementioned apparatus are sealed from the source of hot steam for an equal period of time which results in cooling and condensation of steam that remains confined in the chambers while the operation of the calender is interrupted for a period of approximately twenty minutes. Though the apparatus of Winheim are equipped with means for evacuating condensate from the chambers, a certain period of time subsequent to restarting of the calender is required in order to refill the chambers with fresh steam and to heat the condensate (if any) which has remained in the chambers in spite of the provision of the aforementioned evacuating means. Heating of the condensate results in conversion into hot steam which is ready to be directed through the apertures of the respective wall of the housing to impinge upon the running web or to be admitted into a treating zone between the outer side of the apertured wall and the adjacent side of the path for the running web. As a rule, the quantities of steam which must be directed against a running web in a soft compact calender are relatively small; therefore, the energy contents of such steam do not always suffice to ensure reconversion of condensed steam into steam which is ready to contact the running web. This results in entrainment of droplets of condensed steam by freshly admitted steam, and such droplets act not unlike small missiles or projectiles whose inertia suffices to puncture the running web. Moreover, some droplets of entrained condensed steam deposit on the surface of a soft roll and cooperate with the adjacent hard roll of the soft compact calender to perforate the web in the nip between the soft roll and the hard roll. Such undesirable circumstances are likely to prevail for a reasonably long interval of time subsequent to starting of the calender so that a rather long portion of the running web must be discarded before the expulsion of last traces of condensed steam from the chambers of the apparatus is completed.
German patent application No. 22 03 973 of Pagendarm (published Aug. 9, 1973) discloses a method of and an apparatus for moistening a running web. The apparatus of Pagendarm employs conduits which discharge steam directly against one side of the running web at a location where the other side of the web is contacted by a heated roller or by other propping means. The conduits extend along the inner side of a wall structure which surrounds a compartment. Steam which is discharged by the conduits is caused to rebound and to enter the compartment. The wall structure is or can be heated for the purpose of reducing the likelihood of condensation of steam which enters the compartment subsequent to impingement upon the running web. Alternatively, Pagendarm proposes to provide means for evacuation of condensed steam from the compartment wherein the running web is contacted by steam issuing directly from a plurality of conduits. The proposal of Pagendarm results in considerable reduction of the quantity of condensed steam which can drip onto the running web. However, such undertakings are of no assistance during starting of the apparatus of Pagendarm, i.e., steam which is discharged by the conduits when the operation of the apparatus is restarted is likely to entrain some condensate from the compartment into actual contact with the restarted web.
International patent application No. WO 91/14045 of Sawley et al. (published on Sep. 19, 1991, i.e., subsequent to the priority date of the present application) discloses a steam shower which is to be applied to the upper side of a running web. A steam supplying conduit is provided to admit steam into two channels of pipes One of these channels or pipes serves to heat a set of series-connected steam chambers, and the other channel or pipe serves to admit steam into the first chamber of the set. The apparatus of Sawley et al. exhibits the drawback that droplets of condensed steam are likely to issue from the steam supplying conduit when the operation of the apparatus is restarted. Therefore, the inventors propose to employ screens which consist of wire mesh or the like and are installed in the path of inflowing steam to serve as a means for intercepting the droplets of condensate ahead of the path for the running web. Thus, the proposal of Sawley et al. is intended to prevent existing condensate from reaching the web rather than to prevent the development of droplets of condensed steam.